Controlling selective plugging of carbonaceous strata for controlled production of thermal drive



Sept. 25, 1962 H. w. PARKER 3,055,

CONTROLLING SELECTIVE PLUGGING OF CARBONACEOUS STRATA FOR CONTROLLEDPRODUCTION OF THERMAL DRIVE Filed May 4, 1959 2 Sheets-Sheet 1 AIR BRINEWATER BRINE PRODUCTION 9 RETORTED SHALE 4 25 24 E #7 /WATER \EVAPORATION26 27 44 I COMBUSTION 2025). 22 L2 AIR A x x x F IG.

I M AIR\ 3 FLAME FRjiNT 66 r- 'VAM \yfi "m g Q 7 5 I2 i FIG. 4 iPRODUCTION I '5 innm SALT BLOCK BRINE BRINE INVENTOR. kAlR MRJ J H.W.PARKER BY f! 2;

A f TORNEVS p 1962 H w. PARKER 3,055,423

CONTROLLING SELECTIVE PLUGGING OF CARBONACEOUS STRATA FOR CONTROLLEDPRODUCTION OF THERMAL DRIVE Filed May 4, 1959 2 Sheets-Sheet 2PRODUCTION 5 HOT 52 BRINE GASES- SALT BLOCK "5; PRODUCED AREA FIG. 3

INVENTOR.

H. W. PARKER nyw w A TTORNEVS E FRONT United States Patent 3,d55,i23Patented Sept. 25, 1962 hire CUNERQLLING SELELTEVEE PLUGGING (ll CAR-EQNAEEGUS STRATA FOR QGNTRGLLED PRO- DUQTHBN (BF THERMAL DRIVE Harry W.Par-her, Eartiesviiie, (Eda, assignor to Phillips Petroleum Company, acorporation of Delaware Filed May 4, 1959, Ser. No. 810,919 22 Claims.(Cl. 166-41) This invention relates to the production of hydro carbonsby thermal drive. A specific aspect of the invention is concerned withselective plugging of the carbonaceous stratum while producing same bythermal drive.

In situ combustion in the recovery of hydrocarbons from undergroundstrata containing carbonaceous material is becoming more prevalent inthe petroleum industry. In this technique of production, combustion isinitiated in the carbonaceous stratum and the resulting combustion zoneis caused to move thru the stratum by either inverse or direct air drivewhereby the heat of combustion of a substantial proportion of thehydrocarbon in the stratum drives out and usually upgrades a substantialpro-portion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a boreholetherein followed by injection of air thru the ignition borehole andrecovery of product hydrocarbons and combustion gas thru anotherborehole in [the stratum is a direct iair drive process for effecting insitu combustion and recovery of hydrocarbons from the stratum. In thistype of operation the stratum usually plugs in front of the combustionzone because a heavy viscous liquid bank of hydrocarbon collects in thestratum in advance of the combustion zone which prevents movement of airto the combustion process. To overcome this difficulty and to permit thecontinued progress of the combustion zone thru the stratum, inverse airinjection has been resorted to. By this technique, a combustion zone isestablished around an ignition borehole by any suitable means and air isfed thru the stratum to the combustion zone from one or more surroundingboreholes.

in situ combustion techniques are being applied to tar sands, shale,Athabasca sand and other strata in virgin state, to coal veins byfracturing, and to strata partially depleted by primary and evensecondary and tertiary recovery method-s.

Strata containing hydrocarbon material in the form of solid andsemi-solid and heavy viscous oil are often difiicult to produce becauseof their low permeability. Such strata include shales, heavy tar sands,and those containing semisolid hydrocarbons and/r highly viscous oils.In producing hydrocarbons from such strata around a Well therein bypassing hot gas along the Wall of the well within the stratum, verylittle production can be eflected because of the difiiculty in flowingthe hot gas into the stratum. After producing hydrocarbons from arelatively thin annulus around the well, the hot gases used in heatingthe stratum merely flow along the wall of the Well Without contactingthe deeper solid, semi-solid, and viscous hydrocarbon material.

When producing hydnocarbons irom carbonaceous strata by thermal drivesuch as by in situ combustion wherein the stratum to be produced isignited and the resulting combustion zone is driven thru the stratum,burning a portion of the hydrocarbon material and producing most of thebalance as product, it is desirable in many instances to control thedirection of the movement of the combustion front. Heretofore, noreliable method has been avail-able tor such control.

This invention is concerned with selective plugging of strata containinghydrocarbon material during a thermal drive process for producing thestrata. Accordingly, it is an object 'of the invention to provide animproved process for th production of hydrocarbons from carbonaceousstrata by controlled thermal drive. Another object is to provide athermal drive process which is controllable as to direction and pattern.A further object is to provide a process for producing hydrocarbons froma can bonac-eou-s stratum around a single well therein by thermal drivethru a substantial section of the stratum. Other objects of theinvention will become apparent to one skilled in the art uponconsideration of the accompanying disclosure.

A broad aspect of the invention comprises plugging a selected area of apermeable stratum so as to control the pattern of a thermal driveprocess by heating the area to be plugged to a high temperature andinjecting into the hot stratum a concentrated aqueous solution of asolid compound so as to vaporize water fnom the solution and deposit thecompound in the pores of the stratum until plugging is effected. Anyhighly soluble compound not readily decomposable or volatilizable byheat is operable in the process. Preferred compounds are the relativelycheap and highly soluble salts of sodium and calcium such as sodiumchloride and calcium chloride. Calcium chloride is preferred because ofits greater solubility and hence its greater efficiency in the process.It has been 'found that the addition of a small quantity of glycerin inthe solution greatly raids in rendering the resulting plug impermeableafter cooling. A concentration of glycerin in the range of about 1 to 4volume percent of the solution is eflective in aiding the plugging andrendering the plug impermeable.

A more complete understanding of the invention may be had by referenceto the accompanying schematic drawing of which FIGURE 1 is an elevationin partial section thru a carbonaceous stratum; FIGURE 2 is a similarelevation showing another embodiment of the invention; FIGURE 3 is asimilar elevation showing a third em.- bodiment of the invention; andFIGURE 4 is a plan View of an arrangement of wells nor production by insitu combustion illustrating another embodiment of the invention.

Referring to FIGURE 1, a stratum 10 is penetrated by a well 12, which isprovided with casing 14- extending doWn approximately to the stratum 10and capped by a well head. Within casing 14 are concentric conduits 16,I8, 20, and 22, extending to successively lower levels of the stratum.Packers 24, 25, 26 and 27 pack ofi spaces adjacent the ends of each ofconduits 16, 18 and 20, respectively, for injection of brine in theupper and lower spaces and water in the intermediate space, all of thesespaces being at an intermediate level of stratum 10. Line 30 connectswith tubing 22 for injection of air or hot gas for effecting the thermaldrive. Line 32 connects with conduit 20 for introducing brine to thelowermost packed oif space and line 34 connects with conduit 16 forintroducing brine to the uppermost packed off space at the end ofconduit 16. Line 36 connects with conduit 18 for introducing water intothe intermediate packed oif space at the end of conduit 18. Line 38connects with casing 14 and provides an efiluent line for produced gasescollecting in the outer annulus of the well.

When the arrangement of FIGURE 1 is utilized for production by in situcombustion, a combustion front 40 is driven thru the stratum axiallyaway from Well 12. Numerals 42 and 44 designate salt blocks at the upperand lower levels of the plugged ofl? area.

Referring to FIGURE 2, a stratum 10, which may be a shale or heavy tarsand, is penetrated by a borehole or well 12 which is provided with acasing 14 and a tubing string 22 extending to adjacent the bottom of thehole. A conduit '46 extends from the well head to an intermediate levelof stratum 10 and the well is filled with sand 48 up to the top ofstratum 10. A production line 50 connects with tubing 22 at the wellhead for removal of produced gases. Hot gases and/or air are introducedthru line 52 to casing 14 and the outer annulus of the well. A line 54is connected with conduit 46 for introducing brine to the inner annulus.Numeral 56' designates a fracture formed around well 12, while numeral58 designates a salt block in the stratum adjacent the fracture bothabove and below same.

In FIGURE 3 stratum is penetrated by a pair of spaced apart wells 12 and13 each of which is provided with a casing 14- extending to about thelevel of the top of stratum 10, and with tubing strings 22 and 23,respectively. An air line 30 connects with tubing string 23 and aproduction line 50 connects with tubing string 22. A brine injectionline 60 connects with the annulus of well 12 thru the well head. Packers62 and 64 are positioned around tubing strings 22 and 23, respectively,at a selected intermediate level of stratum 10. A fire front 66 is shownintermediate wells 12 and 13, below the level of packers 62 and 64,moving toward well 13 countercurrently to air injected thru well 13below packer 64. A salt block 58 is shown extending from well 12 towardwell 13 as far as the approximate location of the fire front.

In FIGURE 4, air injection wells 13 are positioned in a ring aroundproduction well 12 with a flame front 66 being driven thru stratum 10 byinverse air injection thru wells 13. Production is recovered thru well12. Brine injection wells are positioned intermediate air injectionwells 13 and production well 12 outside the fire front in a selectedlocation designed to block the movement of the fire front and seal off aselected section of the stratum to fiow of gases.

In producing hydrocarbons from shale, heavy tars, and other bituminousstrata of little or no permeability around a single well, as illustratedin FIGURE 1, air or fuel gasair mixtures are injected thru tubing 22 toestablish in situ combustion in the stratum around the Wall of the well.Of course, it is to be understood that hot gases such as steam, COcombustion gases, nitrogen, etc., may be utilized to retort hydrocarbonsfrom the stratum adjacent the well. Without the use of the invention, itis possible to retort hydrocarbons from only a very thin annulus of thewellbore because of the difficulty of forcing the gases and/ or thecombustion front deeper into the stratum and because heat transferlaterally thru the stratum is exceedingly slow. Naturally, unless somemeans is provided to force the air or other hot gas into the stratum,the same merely passes up the unobstructed borehole without penetratingthe stratum to any appreciable depth. In the embodiment of the inventionshown in FIGURE 1, two layers of brine are injected into the stratumtogether with an intermediate layer of water after the preliminaryretorting and opening of the stratum around the wall of the well as deepas is possible in the open borehole. After this preliminary retorting,injection of air or hot gas is terminated to permit setting of thepackers and conduits preparatory to injecting brine and water.Thereafter, the combustion zone is re-established below packer 27 byconventional means and injection of brine and water is initiated so asto commence plugging of the stratum at the upper level of the upperbrine layer and lower level of the lower brine layer. The hot gases andhot rock in the area of injection of the brine evaporate water from thebrine and leave in the pores of the rock or sand a solid salt blockwhich forces the produced gases and combustion gas deeper into thestratum to bypass the salt block.

The function of the water is to prevent plugging across the advancingface or edge of the injected brine layers by continued evaporation ofwater from the brine. The injection of clear water dissolves any saltblock which [might tend to form in the path of the advancing injectedbrine, thereby allowing forward movement of the brine into the stratumso as to continue forcing the produced hot gases deeper into thestratum.

The pressure applied to the injection of the brine and water iscontrolled in response to the hydrocarbon content of the produced gases.When the hydrocarbon concentration in the produced gases decreases belowa normal production level, it is an indication that the brine and waterare not being forced rapidly enough into the stratum to force the hotgases or combustion front farther into the stratum at a reasonable rate.By properly regulating the air injection rate and the pressure on theinjected liquids, the movement of the salt block and the combustion zonethru the stratum can be controlled so as to drive the combustion frontdeep into the stratum from the ignition well and produce hydrocarbonsfrom the section of stratum above and below the salt block. At any timeduring the process, upon termination of the injection of brine andwater, the combustion zone may be driven around the end of the saltblock and back to the well above the salt block. Of course, it is to beunderstood that the combustion zone may be driven from the well Wallabove the salt block thru the stratum and back to the well wall belowthe salt block by injecting air thin line 38 and recovering productionthru line 30. Indirect drive of the combustion front by inverse airinjection is not operable in the embodiment of the invention shown inFIGURE 1 because it is necessary to drive the hot gases around the endof the injected brine and Water layers in order to open up the stratumto flow of gases and liquids.

The lower limit of the injection pressure on the brine is limited by theconcentration of hydrocarbons in the produced gases. The block should beadvanced at a rate sufiicient to cause the hot gases bypassing the blockto retort hydrocarbons from the area in front of the advancing saltblock rapidly enough to render the process economically feasible.However, advancing the salt block at any appreciable rate makes theprocess operable. The upper limit of brine pressure and rate ofinjection is determined and limited by the air compressors andpermissible air injection pressures at the depth of the stratum beingproduced.

In operating the embodiment of the invention illustrated in FIGURE 2,the wall of well '12 is first produced by retorting hydrocarbonstherefrom with hot gases injected thru line 52 and with production beingrecovered thru tubing 22 and line 50. Brine is then injected thru line54 and conduit 46 where it flows into the hot sand adjacent the end ofconduit 46 and into the permeable stratum opposite the end of theconduit. The evaporation of water from the salt solution by the heat inthe hot sand and rock forms a salt block at levels below and above theend of conduit 46 and in the stratum between these levels. Theintroduction of a salt block into the stratum opposite the end ofconduit 46 forces the hot gases to flow deeper into the stratum in orderto bypass the salt block and thereby produces more tar and hydrocarbonmaterial from the stratum. The resulting salt block eventually blocksthe injection of brine and, in order to overcome this difliculty, thebrine injection pressure is increased until a horizontal fracture 56 isproduced around well 12. This permits the brine to flow into the stratumthru the fracture but the flow of hot gases around the salt block andthe injected brine produces more of the stratum in advance of theinjected brine thereby rendering the same permeable and increasing thedepth to which the brine can penetrate the stratum. The salt block cantherefore be continually extended into the formation along the fractureand the fracture can be increased in radial depth as the injectionprocess is continued, resulting in the production of more tar and otherhydrocarbons from the stratum in front of the advancing fracture andsalt block. It is feasible to either continually inject brine or toinject a large quantity of brine only when the injected gas-tohydrocarbon ratio becomes too high.

The embodiment illustrated in FIGURE 2 is similar to that illustrated inFIGURE 1 in all respects except the manner in which the continuedinjection of brine is assured. The injection of hot gases, includingsteam, is illustrated but it is also feasible to initiate combustioneither above or below the salt block and drive the combustion front thruthe stratum as in the embodiment illustrated in FIGURE 1. It is alsofeasible to utilize in the plugging step any liquid solution or slurryfrom which evaporation leaves a plugging or blocking residue. Toillustrate, in FIGURE 2, the stratum may be fractured by any suitablemeans and a slurry of time clay particles may be used to plug thestratum adjacent the fracture and the sand adjacent the end of conduit46.

The embodiment of the invention illustrated in FIG- URE 3 comprisesinitiating combustion in a selected selection of the stratum such asbelow the level of packers 62 and 64, driving the combustion front thruthe stratum from well 12 to well 13 and injecting the solution effectivein plugging thru line 60 to the annulus above packer 62 so that a saltplug 58 is formed along the upper boundary of the burned out area whichprogresses thru the stratum adjacent the combustion zone as the lattermoves thru the stratum. This embodiment of the invention is applicableonly to strata which are sufficiently permeable to allow the passage ofgases from well to well. It is to be understood that well 12 mayrepresent a central well with a ring of wells 13 surrounding same, orwells 12 and 13 may simply represent wells in a line of production and aline of injection wells, respectively. A combustion front 66 is movedthru the stratum by inverse air injection thru line 3t and tubing 23,while production is recovered thru tubing 22 and line 50.

In the embodiment illustrated in FIGURE 4, a stratum 10 is beingproduced by inverse air injection in a ring pattern of injection wells13 around a central production well 12. It may be desirable to block themovement of the combustion front 66 in a given direction, such as alongthe edge of a cliff, to prevent escape of produced gases or air, oralong the boundary of a field. Brine injection wells 15 are positionedin the vicinity of the desired blocking area and brine is injected sothat the injected air and brine pressure force the brine into thecombustion zone and the hot rock adjacent same whereby evaporation ofthe liquid from the brine deposits suflicient salt to effect plugging.This technique may also be desirable in converting a ring typecombustion front to an in-line combustion front. In the processillustrated, the fire front in the area of the injected brine may besmothered for lack of oxygen, but there is suflicient heat in the hotstratum to vaporize enough water to effect plugging by salt deposition.Rough calculations show for typical conditions using sodium chloride ina given volume of rock after burning that there is sufficient heat tovaporize enough water so that percent of the pore space could be filledby salt crystallizing from a saturated solution. The movement of theresulting slurry further into the hot zone evaporates more water andthereby plugs the formation completely. More highly soluble salts suchas calcium chloride are even more effective. It is also feasible toinject a slug of brine followed by injection of clear water, the brinequantity being sufiicient to effect the blocking and the water servingas the driving fluid. In some instances, the slug of brine may be drivento the desired location in the stratum by injecting gas.

To illustrate the invention a glass tube 9 inches long and %-inch insidediameter was packed with white sand which had a permeability ofapproximately 2.0 darcys. A /s-inch stainless steel tube was placedalong the axis of the glass tube so that a sliding thermocouple could beused to measure the temperature of the sand. The central 6 inches of theglass tube was wrapped with an electric heating tape and covered withapproximately Ai-inch of glass wool insulation. The sand was heated inthis manner to a maximum temperature of 900 F. After the sand had beenheated, brine was injected into the bottom of the tube. When the brinereached a position about 3 inches from the bottom of the tube sufiicientwater had been evaporated to reduce the permeability IOGO-fold or more,and soon there was no further appreciable brine flow.

When cooled, salt blocks formed in this manner tended to leak a smallamount of brine. The injected brine was not saturated therefore itdissolved the salt block. This difficulty was avoided by the addition ofglycerine (2 ml./10fi in solution) to a calcium chloride solution (75gr./ ml. water). The block formed by 24 hours of attempting to flow thissolution into the hot sand remained after cooling of the apparatus.

In other tests the power to the heater was cut off when brine flow wasstarted. In [these cases due to the high heat losses and small thicknessof sand through which the solution flowed no stable permeability blockformed. Tests showed the superiority of a calcium chloride solution (75gr./ 100 ml.) over a sodium chloride solution (30 g./ 100 ml.) to formpermeability blocks under adverse conditions. This is due to (the highersolubility of calcium chloride, and the higher viscosity of theresulting solution.

Various modifications of the invention will occur to one skilled in theart. For example, it is feasible to use as the plugging medium :a liquidwhich decomposes to a solid product when it reaches the hot zone, suchas a solution of water glass (sodium silicate).

Certain modifications or the invention will become apparent in thoseskilled in rthe art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A process for plugging a selected disc-like area of a permeablestratum around a well penetrating said stratum which comprises heatingthe area to be plugged to a temperature substantially above the boilingpoint of the hereinafter described solution at stratum pressure; andinjecting thru said well a concentrated aqueous solution of a compound,solid and stable at said temperature, under pressure, radially into thehot area so as to iorce solution into the pores of said stratum,vaporize water therefrom, and precipitate said compound in the pores ofsaid stratum in said disc-like area until plugging is effected.

2. The process of claim 1 wherein glycerin in the range of about 1 to 4volume percent is incorporated in said solution.

3. The process of claim 1 wherein said compound is calcium chloride.

4, The process of claim 3 wherein glycerin in the range of about 1 to 4volume percent is incorporated in said solution.

5. The process of claim 1 wherein said compound is sodium chloride.

6. The process or" claim 5 wherein glycerin in the range of about 1 to 4volume percent is incorporated in said solution.

7. A process for plugging a selected area of a permeable stratum arounda well penetrating same which comprises extending a conduit from theWell head to the level or" said area; filling ithe annulus around saidconduit and the well below same with sand; heating said sand and saidstratum at the level of said area so a temperature substantially abovethe boiling point of the hereinafter described solution at stratumpressure; and injecting thru said conduit radially in a disc-likepattern into the hot sand and hot stratum adjacent said level aconcentrated aqueous solution of a compound, solid and stable at saidtemperature, so as to vaporize water therefrom and precipitate saidcompound in the interstices within said sand and in rthe pores of saidstratum in said area until plugging is effected.

8. A process nor producing hydrocarbons from a carbonaceous stratumpenetrated by a well, which comprises extending a first conduit from thewell head to a selected intermediate level in said stratum; extending asecond conduit from the well head llJO a lower level in said stratum;filling the annulus within said stratum between the well wall and saidconduits with sand; passing hot gas along the wall of said well withinsaid stratum via said annulus and said second conduit so as to fiuidizeand drive hydrocarbons from the well Wall thereby increasing thepermeability of an annulus of said stratum and heating same to atemperature substantially above the boiling point of the hereinafterdescribed solution at stratum. pressure; thereafiter, continuing thepassing of said gas thru said annulus and While said stratum is at saidtemperature, injecting thru said first conduit radially in a disc-likepattern into the hot sand adjacent the lower end thereof and into theadjacent hot stratum a concentrated aqueous solution of a compound,solid and stable at said temperature, whereby water vaporizes trom saidsolution and said compound is precipitated in said sand and in saidstratum above and below the level of the end of said first conduit so asto form a block to upward and downward flow of said solution; continuingthe passing of said gas thru said annulus and the injection of saidsolution deeper into said stratum so as to force said gas deeper intosaid stratum, thereby continuing the production of hydrocarbons; andrecovering the produced fluids including hydrocarbons from said well.

9. The process of claim 8 wherein said hot gas is passed thru saidsecond conduit and hydrocarbons are recovered \tluu said annulus.

10. The process of claim 9 wherein said hot gas is produced by ignitingsaid stratum below said intermediate level and injectingcombustion-supporting gas th-ru said second conduit so as to effect insitu combustion.

11. The process of claim 8 wherein said compound is calcium chloride.

12. The process of claim 11 wherein glycerin in the range of about 1 to4 volume percent is incorporated in said solution.

13. The process of claim 8 wherein said compound is sodium chloride.

14. The process of claim. 8 wherein said gas comprises steam.

15. The process of claim 8 wherein said gas comprises combustion gas.

16. A process for producing hydrocarbons from a carbonaceous stratumpenetrated by a Well, which comprises establishing in said well at anintermediate level of said stratum an upper solution injection zone, anintermediate water injection zone, and a lower solution injection zone,each being separated and connected with a separate well conduit; heatingan annulus of said stratum immediately surrounding said well to anelevated temperature substantially above the boiling temperature of thehereinafter described solution at stratum pressure by contacting samewith hot gas, thereby producing hydrocarbons from said annulus; whilesaid annulus is at said temperature, injecting a concentrated aqueoussolution of a compound, solid and stable at said temperature, into saidannulus tlu'u said upper and lower injection zones and simultaneouslypassing hot gas thru said annulus between an area above and an areabelow said injection zones, whereby water is vaporized from saidsolution and said compound is precipitated in the pores of said stratumto form solid rings of said compound so as to torce said gas deeper intosaid stratum; injecting water thru said water injection zone so as toprovide tor flow of said solution deeper into said stratum whilecontinuing the injection of said solution and the passing of hot gasthru the expanding annulus, thereby progressively extending said ringsinto said stratum and producing hydrocarbons from deeper in saidstratum; and recovering the produced fluids including hydrocarbons fromsaid well.

17. The process of claim 16 wherein said compound is calcium chlorideand glycerine in the range of 1 to 4 Volume percent is incorporated insaid solution.

18. The process of claim 16 wherein said compound is sodium chloride andglycerine in the range of 1 to 4 volnine percent is incorporated in saidsolution.

19. The process of claim 16 wherein said hot gas is produced by ignitingan annulus of said stratum at a level spaced substantially from saidintermediate level and passing combustion supporting gas directly intothe ignited annulus from said well so as to force resulting hot gas thrusaid stratum around said rings into said well.

20. A process for producing hydrocarbons trom a restricted horizontalsection of a stratum containing hydrocarbons which comprises igniting aselected vertically restricted area of said stratum around an ignitionwell therein; passing combustion-supporting gas to the ignited area soas to move the resulting combustion zone thru said stratum toward atleast one other well therein and produce hydrocmbons trom said stratum;as said combustion zone is advanced radially outwardly from saidignition well injecting a concentrated aqueous solution of a compound,solid and stable at combustion temperature, into said stratum adjacentthe horizontal boundary of said combustion zone so as to vaporize Waterfrom said solution along said boundary and deposit said compound therebyiiorming a solid layer of said compound along said boundary; andrecovery from one of said wells produced fluids including hydrocarbons.

21. The process of claim 20 wherein said compound is calcium chloride.

22. The process of claim 20 wherein said compound is sodium chloride.

References Cited in the file of this patent UNITED STATES PATENTS2,390,770 Barton etal Dec. 11, 1945 2,874,777 Tadema Feb. 24, 19592,881,838 Morse ct a1 Apr. 14, 1959 2,903,065 Holbrook et al. Sept. 8,1959 2,954,218 Dew et al Sept. 27, 1960

